FIELD OF THE INVENTION
The present invention relates, in general, to digital mobile radio systems, and in particular, to a terminal for a digital mobile radio system and to a method for evaluating received data in a terminal for a digital mobile radio system, which offers the capability to reduce the power consumption when receiving information which is not important.
As a rule, time-division multiplexing methods are used for transmitting data in digital mobile radio systems. In this case, the bandwidth which is available on a carrier signal transmitted between base stations and mobile stations is subdivided in time between the various subscribers. Time-division multiplexing and frequency-division multiplexing methods are frequently combined in such a manner that there are a number of carrier frequencies, which are then each accessed separately using the time-division multiplexing method. Thus, for example, in the GSM system (Global System for Mobile Communications), carrier frequencies with a spacing of 200 kHz from one another are used, which are subdivided into eight time slots or data packets. In this case, data is frequently transmitted to the mobile stations from the base stations which is important for only a single one of the mobile stations, or for none of them. However, conversely, this can also relate to data packets which are sent from a mobile station to a base station. Data packets which are not important may in this case be data packets which contain so-called dummy data or filling data, but they may also be data packets which contain information that does not relate, or no longer relates, to the received terminal since, for example, the terminal has already received it once. In the prior art, all of the transmitted data is received by the receiving terminal and is processed irrespective of whether the data is or is not required by the terminal. This results in increased power consumption in the terminal which is disadvantageous, particularly for mobile stations powered by batteries such as rechargeable batteries.
Published international patent application, WO 96/37051 discloses a method and an apparatus for saving power in portable battery-powered radio appliances. In this case, a received message is compared with a previous received message. If the two messages match, the radio appliance is switched to a power saving mode, in which the message received later is not processed any further. Published international patent application, WO 94/08432 discloses a method for transmitting information between a base station and a mobile station in a digital control channel of a telecommunications system. In this case, the base station transmits change characters which indicate whether successive messages differ. The mobile station processes received messages only if a previous change character indicates a change in comparison to the previous messages. Published international patent application, Wo 94/27377 discloses a mobile station for a mobile radio system, having a receiving device for receiving digital data packets and for providing soft decision values for received data packets, and having a decision device which, before complete reception of an information unit comprising one or more data packets, uses a part of the information unit which has already been received to decide whether the information unit is or is not important and, if the decision is that the information unit is not important, causes the receiving device to ignore the rest of the information unit. In this case, the soft-decision values are used to determine whether a received data packet is or is not free of errors. If the data packet is free of errors, a power saving signal is produced.
The received data packet is furthermore compared with expected or predetermined data in order to determine whether the data packet contains information which is or is not important for the mobile station. If the information is not important, the mobile station is switched to a power saving mode, in which the rest of the received data packets are not processed any further.